Method for producing nano-carbon composite

ABSTRACT

A method for producing a nano-carbon composite is provided. The method includes mixing nano-carbon powder and matrix alloy powder by milling, to provide a mixed powder and substantially evenly penetrating the nano-carbon powder inside of the matrix alloy by milling the mixed powder. In addition, the method includes clustering the mixed powder by milling the mixed powder slower than in the penetrating process.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority of Korean Patent ApplicationNumber 10-2013-0158796 filed Dec. 18, 2013, the entire contents of whichapplication is incorporated herein for all purposes by this reference.

TECHNICAL FIELD

The present invention relates to a method for producing a nano-carboncomposite, which secures easy oxidation and dispersion thereof andminimizes damage and oxidation in molten metal of carbon nano tube (CNT)or carbon nano fiber (CNF) by artificially enlarging particle size ofthe nano composite powder through milling condition change, inparticular, by conducting ball milling.

BACKGROUND

A typical aluminum composite in which CNT or CNF is dispersed has beengenerally produced by sintering and extruding processes through powdermolding. Moreover, some composite for casting has been produced bypreparing composite powder to prevent powder oxidation and floating;conducting intermediate process to form the pellet; and charging thepellet in molten metal.

In particular, a typical method using the composite powder generallyproduces a nano-carbon dispersed composite by preparing composite powderof nano-carbon and matrix alloy through high energy ball milling;preparing intermediate material in the form of pellet (green compact)through sintering or press; and charging the pellet in molten metal.However, the above-mentioned method may raise problems, such asinefficiency and high production cost, since the intermediate processfor pellet preparation costs additional time and efforts.

The description provided above as a related art of the present inventionis merely for helping understanding the background of the presentinvention and should not be construed as being included in the relatedart known by those skilled in the art.

SUMMARY

The present invention provides a technical solution to theabove-described problems associated with conventional methods.

In one exemplary embodiment, the present invention provides a method forproducing a nano-carbon composite, which may include: mixing nano-carbonpowder and matrix alloy powder by milling, to provide a mixed powder;substantially evenly penetrating the nano-carbon powder inside of thematrix alloy by milling the mixed powder; and clustering the mixedpowder by milling the mixed powder slower than in the penetrating step.

The nano-carbon powder may contain at least one of CNT and CNF. Themilling condition in the mixing step may be about 40 to 60 RPM for about8 to 11 hours. The milling condition in the penetrating step may beabout 500 to 700 RPM for about 2 to 3 hours. The milling RPM in thecoarsening step may be about 75 to 85% of the milling RPM in thepenetrating step. The milling condition in the coarsening step may beabout 450 to 500 RPM for 40 to 70 min. The matrix alloy powder may be analuminum alloy powder.

In another exemplary embodiment, the nano-carbon composite produced bythe method of the present invention may include particles in the size ofabout 400 μm or greater.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features of the present invention will now bedescribed in detail with reference to certain exemplary embodimentsthereof illustrated the accompanying drawings which are givenhereinbelow by way of illustration only, and thus are not limitative ofthe present invention, and wherein:

FIG. 1 is an exemplary microscopic view showing the nano-carboncomposite particles in the size of about 400 μm or less according to oneexemplary embodiment of the present invention;

FIG. 2 is an exemplary microscopic view showing the nano-carboncomposite particles in the size of about 400 μm or greater according toanother exemplary embodiment of the present invention;

FIG. 3 is an exemplary microscopic view showing CNT penetrates inside ofthe matrix powder of the nano-carbon composite according to oneexemplary embodiment of the present invention; and

FIG. 4 is an exemplary graph showing a correlation between the hardnessof particles and the particle size of the nano-carbon compositeaccording to one exemplary embodiment of the present invention.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousexemplary features illustrative of the basic principles of theinvention. The specific design features of the present invention asdisclosed herein, including, for example, specific dimensions,orientations, locations, and shapes will be determined in part by theparticular intended application and use environment. In the figures,reference numbers refer to the same or equivalent parts of the presentinvention throughout the several figures of the drawing.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items.

Unless specifically stated or obvious from context, as used herein, theterm “about” is understood as within a range of normal tolerance in theart, for example within 2 standard deviations of the mean. “About” canbe understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%,0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear fromthe context, all numerical values provided herein are modified by theterm “about”.

Hereinafter, the exemplary embodiments of the present invention now willbe described in detail with reference to the accompanying drawings.

FIG. 1 is an exemplary microscopic view showing the nano-carboncomposite particles in the size of about 400 μm or less in one exemplaryembodiment of the present invention; FIG. 2 is an exemplary microscopicview showing the nano-carbon composite particles in the size of about400 μm or greater according to another exemplary embodiment of thepresent invention; and FIG. 4 is an exemplary graph showing acorrelation between the hardness of particles and the particle size ofthe nano-carbon composite according to one exemplary embodiment of thepresent invention.

In one exemplary embodiment of the present invention, the method forproducing the nano-carbon composite may include: a mixing step formixing nano-carbon powder and matrix alloy powder by milling, to providea mixed powder; a penetrating step for substantial evenly penetrating ofthe nano-carbon powder inside of the matrix alloy by milling the mixedpowder; and a coarsening step for clustering the mixed powder by millingthe mixed powder slower than in the penetrating step. In certainexemplary embodiments, the nano-carbon powder may contain at least oneof CNT and CNF.

In addition, the milling condition in the mixing step may be about 40 to60 RPM for 8 to 11 hours; and the milling condition in the penetratingstep may be about 500 to 700 RPM for about 2 to 3 hours. The milling RPMin the coarsening step may be about 75 to 85% of the milling RPM in thepenetrating step. In addition, the milling condition in the coarseningstep may be about 450 to 500 RPM for about 40 to 70 min. The matrixalloy powder may be an aluminum alloy powder and the nano-carboncomposite produced by the method of the present invention may includeparticles in the size of about 400 μm or greater.

According to the exemplary embodiment of the present invention, thenano-carbon composite may be produced by a casting process for massproduction. In such a method, high energy ball milling may be conductedusing a mechanical mixing method to remove an intermediate pelletprocess. Thus, oxidation and dispersion of the nano composite may bemore easily secured by artificially enlarging particle size of the nanocomposite powder with changes in milling condition. The presentinvention further provides such a process which may minimize damage andoxidation in molten metal of CNT or CNF.

In one exemplary embodiment of the present invention, the method forproducing coarse powder of the aluminum nano-carbon composite in which anano-carbon such as CNT or CNF is dispersed may include: mixing CNT ofabout 10 to 15 wt % or CNF of about 10 to 15 wt % and aluminum alloypowder by a first slow milling at about 50 RPM for 10 hour; milling ofhigh energy ball milling (HEM) at about 600 RPM for 2 to 3 hours; andmilling at about 480 RPM, which may be reduced for about 20% from theRPM of the second milling, for 1 hour for powder coarsening. Inparticular, the first slow milling may improve the clustered state ofthe CNT or CNF, and the second high energy milling may penetrate theCNT/CNF inside the aluminum powder using cold welding using high energy.The third powder coarsening milling may obtain powder in the particlesize of about 400 μm or greater by clustering aluminum powder.

Further, the nano composite powder may be charged while stirring withmolten metal, to produce aluminum composite for casing in which theCNT/CNF may be dispersed. Therefore, intermediate process for pelletprocessing may be removed by the powder coarsening process. Accordingly,by the methods of the exemplary embodiment of the present invention,mass production of the nano-carbon composite may be simplified, the costfor production thereof may be reduced, and a melting time may be reducedby charging the powder itself in the molten metal.

FIG. 1 shows an exemplary microscopic view of particles in the size of400 μm or less, and FIG. 2 shows exemplary composite particles in thesize of 400 μm or greater according to the exemplary embodiment of thepresent invention. Furthermore, according to the exemplary embodiment ofthe present invention, CNT may penetrate the matrix powder material asshown in FIG. 3.

Additionally, FIG. 4 is an exemplary graph showing a correlation betweenthe hardness of particles and the particle size of the nano-carboncomposite. As shown in FIG. 4, from the hardness test results among aspecimen produced by using pure aluminum, a specimen produced usingpowder in the size of about 400 μm or less and a specimen produced byusing powder in the size of about 400 μm or greater, the hardness of thespecimen produced using powder in the size of about 400 μm or greater isincreased for about 150% against the specimen of pure aluminum matrix,and is equal to or greater than the hardness of the specimen producedusing powder in the size of about 400 tm or less.

According to the method for producing the nano-carbon composite havingthe characters described above, in particular, when conducting ballmilling, oxidation and dispersion may be more easily maintained byartificially enlarging particle sizes of the nano composite powderthrough milling condition change, and damage and oxidation in moltenmetal of CNT or CNF may be minimized. In particular, since theintermediate pellet producing process may be removed, the processefficiency may be improved, and time and cost for producing thecomposite may be reduced.

The invention has been described in detail with reference to exemplaryembodiments thereof. However, it will be appreciated by those skilled inthe art that changes or modifications may be made in these exemplaryembodiments without departing from the principles and spirit of theinvention, the scope of which is defined in the appended claims andtheir equivalents.

What is claimed is:
 1. A method for producing a nano-carbon composite,comprising: mixing nano-carbon powder and matrix alloy powder bymilling, to provide a mixed powder; substantially evenly penetrating thenano-carbon powder inside of the matrix alloy powder by milling themixed powder; and clustering the mixed powder by milling the mixedpowder slower than in the penetrating process.
 2. The method forproducing the nano-carbon composite of claim 1, wherein the nano-carbonpowder includes at least one of a group selected of: carbon nano tube(CNT) and carbon nano fiber (CNF).
 3. The method for producing thenano-carbon composite of claim 1, wherein the milling condition in themixing step is about 40 to 60 RPM for about 8 to 11 hours.
 4. The methodfor producing the nano-carbon composite of claim 1, wherein the millingcondition in the penetrating step is about 500 to 700 RPM for about 2 to3 hours.
 5. The method for producing the nano-carbon composite of claim1, wherein the milling RPM in the clustering step is about 75 to 85% ofthe milling RPM in the penetrating step.
 6. The method for producing thenano-carbon composite of claim 1, wherein the milling condition in theclustering step is about 450 to 500 RPM for about 40 to 70 min.
 7. Themethod for producing the nano-carbon composite of claim 1, wherein thematrix alloy powder is aluminum alloy powder.
 8. The method forproducing the nano-carbon composite of claim 1, wherein the nano-carboncomposite includes particles in a size of about 400 μm or greater.